In the manufacture of paper, a very dilute slurry of about 99% water and 1% papermaking fibers is ejected at very high speed and precision from a headbox onto a moving forming fabric. The slurry is rapidly dewatered through the fabric to a consistency of roughly 25% fiber as it proceeds downstream through the forming section and then to about 45% fiber as it passes through the press section of the papermaking machine. The forming section is often referred to as the “wet end” of the papermaking machine because of the relatively large volume of water that must be removed from the embryonic web and managed during the papermaking process. Means for doing this are well known and consist, in modern papermaking machines, of blades or foils which are mounted on the covers of dewatering boxes located opposite the sheet, or on felt cleaning or steam heating boxes in the press section. The surfaces of these blades (known variously in the industry as foil blades, foils, forming board blades, uhle box blades, dewatering blades, lovac blades, suction box blades and deflector blades, henceforth referred to simply as “blades”) are in constant sliding contact with the papermaking fabrics transporting the web. The wear surfaces of these blades are typically made from a ceramic material so as to resist for as long as possible the abrasive wear caused by factors including the constant movement of the fabrics, and abrasive substances in the slurry.
Ceramic covered blades as used in the papermaking industry are currently manufactured using one of two techniques. The first is to bond individual ceramic segments (usually 0.5″ to 3″ [1.2-7.5 cm] long) into a full length fiberglass support base (full length meaning the base extends across the full width of the paper machine for which it is intended) and then to precision grind this ceramic assembly to a finished condition. The second technique is to finish grind the individual ceramic segments first, and then mount them into an accurately machined base that can be made of fiberglass or polyethylene, the choice of which will depend on the end use and customer preference. In both cases, the blade is produced as a full length product. It will be appreciated that this can be a very time consuming, expensive and laborious process as these full length blades must be made to a length sufficient to span the width of a modern papermaking machine; such machines may have widths as great as 400 inches (10.2 m) or more.
Currently, in order to repair a bonded style blade (where individual ceramic segments are bonded directly onto the full length base), the only solution is to heat the ceramic segments in order to destroy the adhesive bond between base and segment, and then remove the damaged segments. This frequently results in damaging additional segments adjacent to the intended repair site. After the damaged segments are removed, replacement segments are then bonded back in the original location. These replacement segments then have to be hand ground to correspond as accurately as possible with the configuration of the existing segments. Frequently, re-bonding is not as durable as the original bond, increasing the potential for future failure.